The present invention relates to spectrometry, and more specifically to a non-dispersive spectrophotometer adapted to detect the presence of SO.sub.2 in a sample, regardless of the presence therein of NO.sub.2.
It is a well-known phenomenon that the atoms or molecules of a given material may absorb electromagnetic radiation at specific frequencies, the frequencies and relative intensity of the radiation absorption comprising the spectral "signature" of the material. This characteristic may be utilized to identify the presence of a given material by directing radiation upon it, and noting the degree and/or wavelength at which the radiation is attenuated.
In recent years the urgency of controlling, and indeed reducing, the incidence of pollutants in the atmosphere has become apparent. Long-known apparatus have been modernized, and new apparatus devised, in order to meet stringent requirements placed upon both government and industry for controlling and lessening the output of pollutants including those transferred to the atmosphere by smoke, flue gases, and other vaporous effluences from industrial and other processes.
In order to monitor the operation of these devices, and to detect the presence of certain specified polluting agents, analytical apparatus is needed. Although various types of apparatus have long been known they have typically taken the form of laboratory apparatus which, though highly accurate, are very expensive and often ill-suited for day-to-day usage in an industrial environment, often by semi-skilled personnel.
Many efforts have been directed toward the provision of pollution detecting apparatus which fulfill the above-described need. Any one of a number of physical principles may be utilized to achieve the desired analysis; conductometric, colormetric, coulemetric, electrochemical transducers, photoemission, flame photometric, thermoconductivity, infared, and ultraviolet light absorption of both the dispersive and non-dispersive types are available, and have long been known in the art. Of all the foregoing approaches, the one which is believed to show the most promise for fulfilling commercial needs is the ultraviolet absorption type. In U.S. Pat. No. 2,350,001-Van Den Akker, for instance, a recording device is shown which utilizes the spectral absorbing properties of a gas or vapor to detect its presence. An ultraviolet light source has its beam split into two elements, which traverse two physically separate paths or channels; suitable filter means is used to selectively attenuate the radiation to facilitate the process. In one embodiment, a fluorescent plate is used to obtain light at a predetermined wavelength in response to the impingment thereon of ultraviolet light at a second wavelength. U.S. Pat. No. 3,778,162-Gant et al discloses means for measuring the amount of mercury vapor present in a sample and uses a pair of channels for comparing the transmission of ultraviolet light, one of said channels having therein a reservoir of mercury vapor. U.S. Pat. No. 3,819,945-Egan et al teaches a spectrometer for detecting the presence of nitric oxide (NO) by identifying a portion of its spectral signature. Mechanical choppers are used for periodically interrupting a beam of impingent light and a grating diffracts the light, spreading it into a spectrum so that predetermined wavelengths thereof may be selected by means of a mechanical shutter. The foregoing approaches, while presumably effective, nonetheless have the deficiency of being expensive and/or complex.
The present invention teaches an improved spectrometer for analyzing a gaseous sample particularly for the presence of SO.sub.2 through the use of a two-channel approach; but without the need for an expensive redundant system of lenses, sample chambers, etc. Further, with the approach taught herein, a selected material may be identified by its spectral absorption characteristics without the need for diffraction gratings, movable shutters, mechanical choppers, and the like. Moreover, the foregoing desideratum is achieved with the use of a relatively inexpensive, commercially available light source.
It will therefore be understood that one object of the present invention is to provide an improved gaseous analyzer of the non-dispersive, absorption type.
It is another object of the present invention to provide a practical spectrophotometer which is substantially simpler in operation than those heretofore known.
Still another object of this invention is to provide an improved spectrophotometer analyzer which can be inexpensively constructed yet has the precision necessary for identifying undesirable levels of a specified pollutant.